Third harmonics due to surface barrier in high-temperature superconductor

Abstract

The influence of surface barrier on the third harmonics ac susceptibility ͑ 3 ͒ is studied numerically. The surface barrier is described by a critical current density in surfaces which are higher than the inside one. The model can act as the critical state one, the flux creep one, or the flux flow one when temperature ͑or field͒ changes. The numerical results based on the model are more close to the popular experimental data probing the harmonics as a function of temperature ͑or field͒. Besides, the surface barrier will lead to new peaks in the real and imaginary parts of the third harmonics, which are the finger signature of the surface barrier. Comparison of the peaks with those of the real part of elemental harmonic shows that they are located at the same temperature where dips in Ј caused by the surface barrier occur, which is in well agreement with experiments.

Investigation of the vortex dynamics of Fe1.02Se crystals by fundamental and 3rd harmonic ac magnetic susceptibility analysis

“…There is an extreme diversity of (linear and non-linear) processes, which drives the magnetic response and evolve with the H ac change [89]. Fine examples are the formation at low ac amplitudes [72,105,[119][120][121] of geometrical [122] or surface (current) barriers [123,124], which hinder the penetration of the vortices (in the case of weak bulk pinning abilities of the superconductor).…”

Harmonic AC magnetic susceptibility analysis of FeSe crystals with composite morphology

“…This effect introduces a further distortion of the field at the edge of the crystals when the magnetic field is applied perpendicular to the plane [49][50][51] and it is also visible for other investigated samples [21]-FeSe #2, as reported in the inset of figure 2. In addition, it causes an irreversibility in the entry/exit of the vortices during the AC magnetic field cycle [47,52,53].…”

Complex AC Magnetic Susceptibility as a Tool for Exploring Nonlinear Magnetic Phenomena and Pinning Properties in Superconductors

“…We can extend the list of phenomena accessible by the ACMS considering the Bean-Livingston, edge and geometrical barriers [20][21][22][23], the Josephson effects [24], the vortex avalanches [25] and the Campbell regime [16] (in the presence of the reversible oscillation of the vortices inside the pinning potential wells).…”